The invention of the present application is related to ring laser angular rate sensors employing a passive ring resonator.
The Sagnac effect is well known in the art of ring laser angular rate sensors. In such sensors, a linear relationship is established between the rate of rotation of a closed-loop waveguide structure and the difference in frequency of oppositely directed electromagnetic waves traveling therein. In the art, there exists two types of waveguide structures: (i) active ring resonators and (ii) passive ring resonators.
Active ring resonator systems are well known in the art and are described in U.S. Pat. No. 3,373,650 by Killpatrick. An active ring resonator is one in which the resonator itself is part of an electromagnetic wave oscillator for generating two oppositely traveling electromagnetic waves within the resonator. In U.S. Pat. No. 3,373,650, a laser gain medium is located within an optical closed-loop path for generating counter-propagating laser beams, the optical closed-loop path defining a resonant cavity waveguide structure. In active ring resonator systems, the rate of rotation of the closed-loop path determines the frequency of the counter-propagating waves since the effective closed-loop path length determines the frequency of the wave produced by the integral oscillator.
Passive ring resonator systems are also well known. U.S. Pat. No. 4,135,822 by Ezekiel, and U.S. Pat. No. 4,326,803 by Lawrence describe a passive ring resonator system. An electromagnetic wave source external to the resonator is coupled to a ring resonator structure to produce counter-propagating waves within the structure. In passive ring resonator systems, the frequency of the beams is solely dependent on the electromagnetic wave source. The rate of rotation of the closed-loop path dictates which frequencies are allowed to propagate within the resonant structure.
In each of the foregoing passive ring resonator patents, a laser beam is coupled to a passive ring resonator. The frequency of the laser beam is adjusted to determine the resonant frequency of the optical closed-loop path for each propagation direction. The difference between the resonant frequencies of each direction of propagation is indicative of the rotation rate of the closed-loop path or passive ring resonator.